Add .vscode extension recommendations

[pkbullock]

This is for Visual Studio Code extensions

• Top Level of Repo for M365 Toolkit, Adaptive Card Previewer
• Include Power Platform extension extension
• Sample Level as well.

[garrytrinder]

This would be useful if you clone the full repo, but we should also consider reviewing the recommended extensions for each sample as developers can download individual samples from the adoption site.

[pkbullock]

I have noticed that quite a few samples have .vscode folders, possibly as part of the ATK setup, but there are some without.

[pkbullock]

I've added those now, are there any others you would recommend @garrytrinder @sebastienlevert ?

[sebastienlevert]

I would keep the default ones created by the original apps / extensions.